Add some UI to be able to let the user choose whether to enable Windows Service or not.

This decision was taken in an admin meeting and the main reasons are that there are lots of users that may dislike the idea of OpenDS modifying the Windows Service Registry as they are not using it in production (yet).

Moreover there is a bug (1603) that prevents registering the server as a service on Vista, so these modifications will allow to the users to use the graphical setup on that OS.